An engine is a device that generates mechanical motion. In general, an engine is any electromechanical device that converts energy, including electrical, chemical, heat, or any other type of energy, into mechanical motion. This includes, for example, internal combustion engines, steam engines, Carnot engines, Stirling engines, etc. A cyclo-mechanical engine is any engine that operates on a cycle to generate mechanical motion.
Internal combustion engines typically have one or more cylinders in which mechanical energy is generated by combustion of flammable materials. In an internal combustion engine, a piston is typically movably positioned within the cylinder and connected to a crankshaft by a rod. The movement of the piston turns the crankshaft providing motive force to the wheels of the vehicle.
Engines typically operate using a four stroke combustion cycle, also known as the Otto cycle. The four strokes are: 1) the intake stroke, where the piston moves from an in position to an out position, drawing fuel and air into the cylinder; 2) the compression stroke, where the piston moves from the out position to the in position, compressing the fuel and air mixture in the cylinder; 3) the combustion stroke, where a spark plug emits a spark, igniting the fuel and air mixture, causing an explosion that propels the piston to the out position; and 4) the exhaust stroke, where the piston moves back to the in position, forcing the exhaust fumes from the cylinder. Valves permit the introduction of fuel and air, and another valve allows the expulsion of the exhaust fumes.
The combustion cycle is made inefficient when a misfire occurs. A misfire is sometimes thought of as the total lack of combustion in a cylinder. More broadly, however, a misfire occurs any time the firing of a cylinder fails to release an expected amount of energy. A misfire, therefore, can be thought of as a total or partial lack of combustion in a cylinder.
Misfires can occur for many different reasons. For example, the spark plug may not be providing a spark to the compressed fuel/air mix. A bad fuel mix, which may be the result of a clogged fuel injector, a clogged air intake, or both, can cause a misfire to occur. Essentially, the fuel and the air are not being introduced into the cylinder in the proper ratio to achieve optimal combustion. A lack of compression, such as when the seals in the cylinder fail and allow the fuel/air mixture to leak out as the piston attempts to compress the mixture, can also lead to a misfire. Many other factors can contribute to a lack of complete combustion.
Misfires are a cause for concern for vehicle operators. When a misfire occurs, the fuel in the cylinder does not combust and is sent out the exhaust valve. This unburned fuel then passes out through the exhaust system of the vehicle. This results in lower fuel efficiency as well as additional wear and tear on catalytic converters.
Misfires, particularly those accompanied by partial combustion, may be difficult to detect.